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United States Patent |
6,212,110
|
Sakamoto
,   et al.
|
April 3, 2001
|
Semiconductor memory device
Abstract
Switch MOSFETS are interposed between a sense amplifier disposed in a
dynamic RAM and complementary bit lines. After signal voltages were read
out by the selecting operations of the word lines from a plurality of
dynamic memory cells selected, to the plurality of pairs of complementary
bit lines in accordance with their individual storage informations, the
switch control signal of the switch MOSFETs is changed from a select level
to a predetermined intermediate level. The switch MOSFETs, supplied with
the intermediate potential at their gates, are turned ON as a result that
sense nodes are set to one level in accordance with the amplifying
operations of the sense amplifier. An amplification signal generated by
the amplifying operation is transmitted through the column select circuit
to input/output lines in response to the column select signal, and the
switch control signal is returned from the intermediate potential level to
the select level in response to the selecting operation of the column
select circuit.
Inventors:
|
Sakamoto; Tatsuya (Higashimurayama, JP);
Nagashima; Osamu (Hamura, JP);
Takemura; Riichiro (Kokubunji, JP)
|
Assignee:
|
Hitachi, Ltd. (Tokyo, JP)
|
Appl. No.:
|
471504 |
Filed:
|
December 23, 1999 |
Foreign Application Priority Data
| Dec 24, 1998[JP] | 10-365887 |
Current U.S. Class: |
365/190; 365/207; 365/208 |
Intern'l Class: |
G11C 007/00 |
Field of Search: |
365/63,190,205,207,208
|
References Cited
U.S. Patent Documents
5262999 | Nov., 1993 | Etoh et al.
| |
5265058 | Nov., 1993 | Yamauchi.
| |
5875141 | Jan., 1999 | Shirley et al. | 365/207.
|
5959913 | Sep., 1999 | Raar | 365/201.
|
6084816 | Jul., 2000 | Okamura | 365/230.
|
6118708 | Sep., 2000 | Yoshida et al. | 365/190.
|
Foreign Patent Documents |
64-73596 | Mar., 1989 | JP.
| |
4-167293 | Jun., 1992 | JP.
| |
5-62463 | Mar., 1993 | JP.
| |
8-106781 | Apr., 1996 | JP.
| |
10-241367 | Sep., 1998 | JP.
| |
11-086549 | Mar., 1999 | JP.
| |
Primary Examiner: Nelms; David
Assistant Examiner: Auduong; Gene N.
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus, LLP.
Claims
What is claimed is:
1. A semiconductor memory device comprising:
a plurality of word lines, with which address select terminals of a
plurality of dynamic memory cells are individually connected;
a plurality of pairs of complementary bit lines, with which a plurality of
dynamic memory cells are individually connected;
a plurality of pairs of transmission MOSFETs interposed between said
plurality of pairs of complementary bit lines and a plurality of pairs of
sense nodes for receiving a control signal at their gates;
a plurality of sense amplifiers having their individual input/output
terminals connected with said plurality of pairs of sense nodes and
adapted to be fed with an operating voltage in response to an operation
timing signal; and
data output lines, with which said sense nodes are connected through a
column select circuit to be switch-controlled by a column select signal,
wherein the voltage level of said control signal can be selectively set to
one of a select level, an unselect level and an intermediate level,
wherein after signal voltages were read out by the selecting operations of
said word lines from the dynamic memory cells to the plurality of pairs of
complementary bit lines in accordance with their individual storage
informations, said control signal is changed from the select level to the
intermediate level,
wherein said sense amplifiers are fed with an operating voltage to start
the amplifying operations in response to the change of said control signal
to the intermediate level,
wherein an amplification signal generated by said amplifying operation is
transmitted through the column select circuit to said input/output lines
in response to the column select signal,
wherein said control signal is returned from the intermediate level to the
select level in response to the selecting operation of said column select
circuit, and
wherein paired transmission MOSFETs for receiving the signal of said
intermediate level at their gates are adapted such that they have an OFF
state or a relatively high ON resistance, in the state where the signal is
read out from the memory cells to said complementary bit lines, and such
that one of them has an ON state or a relatively low resistance whereas
the other has the OFF state or the relatively high ON resistance, in the
state where the signal of the sense nodes is amplified by the amplifying
operations of the sense amplifiers.
2. A semiconductor memory device according to claim 1,
wherein a precharge circuit for precharging said complementary bit lines is
further provided and connected with said sense nodes,
wherein when said word lines are in an unselected state, said control
signal is set to a select level so that the complementary bit lines are
precharged through said transmission MOSFETs by the precharge circuit
disposed at the sense nodes.
3. A semiconductor memory device according to claim 1 or claim 2,
wherein the complementary bit lines are arranged on the left and right
sides around said sense nodes,
wherein transmission MOSFETs are used with select switch MOSFETs of said
complementary bit lines arranged on the left and right, and
wherein the switch control signal of the transmission MOSFETs,
corresponding to the unselected complementary bit line, is set to an
unselect level before said word lines are selected.
4. A semiconductor memory device according to claim 3,
wherein said control signal is returned in a gentler change from said
intermediate level to the select level in response to the selecting
operation of said column select circuit than that from the select level to
the intermediate level.
5. A semiconductor memory device according to claim 3,
wherein the main amplifier including the CMOS latch circuit having
connected input/output terminals is connected with said data output lines,
wherein said data output lines are precharged to the other level of a
polarity reversed from that of one level of said sense nodes, and
wherein said main amplifier feeds, when it is brought into the operating
state, said CMOS latch circuit with an operating voltage corresponding to
the other potential.
6. A semiconductor memory device according to claim 3,
wherein said word lines include a main word line and a plurality of sub
word lines assigned commonly to said main word line,
wherein the gates of the address select MOSFETs of said dynamic memory
cells are connected with said sub word lines,
wherein one of said sub word lines is selected by a sub word driver which
receives the signal of said main word line and the signals of said sub
word selecting lines,
wherein said sub word driver generates a select signal of the sub word
lines which are disposed on the left and right sides excepting the end
portions of the memory cell array, and
wherein said sense amplifiers sense the amplified signals from the
complementary bit lines which are disposed on the left and right sides
excepting the end portions of the memory cell array.
7. A semiconductor memory device according to claim 3,
wherein the operating voltage to be fed to said sense amplifiers is a
dropped voltage which is dropped from the power voltage fed from an
external terminal,
wherein the select level of said word lines and the select level of said
transmission MOSFETs are a boosted voltage which is boosted from said
power voltage; and
in that said intermediate level uses the dropped voltage corresponding to
the operating voltage of said sense amplifiers.
8. A semiconductor memory device comprising:
a plurality of word lines;
a pair of complementary bit lines;
a plurality of memory cells individually connected with said plurality of
word lines;
a sense amplifier for amplifying a read signal which is caused to appear on
said pair of complementary bit lines when a memory cell is selected; and
a pair of MOSFETs interposed between a pair of sense nodes of said sense
amplifier and said pair of complementary bit lines, which receives a
control signal at their gates,
wherein said control signal can be selectively set to one of a select
level, an unselect level and an intermediate level,
wherein after said read signal has appeared on said pair of complementary
bit lines, said control signal is changed from said select level to the
intermediate level, and
wherein after the start of the operation of said sense amplifier, said
control signal is returned from said intermediate level to said select
level.
9. A semiconductor memory device according to claim 8,
wherein said pair of MOSFETs receiving the control signal of said
intermediate level at their gates are adapted such that they have an OFF
state or a relatively high ON resistance, in the state where said read
signal appears on said pair of complementary bit lines, and such that
one-MOSFET of said pair of MOSFETs has an ON state or a relatively low ON
resistance whereas the other MOSFET has the OFF state or the relatively
high ON resistance, in the state where the signal of said one pair of
sense nodes is amplified by the operations of the sense amplifier.
10. A semiconductor memory device according to claim 9,
wherein said pair of MOSFETs receiving the control signal of said select
level at their gates are turned ON, and
wherein said pair of MOSFETs receiving the control signal of said unselect
level at their gates are turned OFF.
11. A semiconductor memory device comprising:
a first memory array including a plurality of first word lines, a pair of
complementary bit lines intersecting said plurality of first word lines,
and a plurality of memory cells;
a second memory array including a plurality of second word lines, a pair of
complementary bit lines intersecting said plurality of second word lines,
and a plurality of memory cells;
a sense amplifier shared between said first memory array and said second
memory array for amplifying a read signal which is caused to appear on a
pair of corresponding complementary bit lines when a memory cell is
selected; and
MOSFET pairs individually interposed between a pair of sense nodes of said
sense amplifier and the pair of complementary bit lines on the side of
said first memory array and between said pair of sense nodes and the pair
of complementary bit lines on the side of said second memory array,
wherein the gate voltage of each of the MOSFET pairs can be selectively set
to one of a select level, an unselect level and their intermediate level,
wherein when the memory cell of said first memory array is selected, the
gate voltage of the MOSFET pairs on the side of said second memory array
is set to the unselect level,
wherein when the memory cells of said second memory array are selected, the
gate voltage of the MOSFET pairs on the side of said first memory array is
set to the unselect level,
after said read signal has appeared on said pair of complementary bit
lines, the gate voltage of the corresponding MOSFET pairs is changed from
said select level to said intermediate level, and
wherein after the start of the operation of said sense amplifier, the gate
voltage of the corresponding MOSFET pairs is returned from said
intermediate level to said select level.
12. A semiconductor memory device according to claim 11,
wherein said MOSFET pairs receiving the gate voltage of said intermediate
level are adapted such that they have an OFF state or a relatively high ON
resistance, in the state where said read signal appears on said pair of
complementary bit lines, and such that one MOSFET of said MOSFET pairs has
an ON state or a relatively low resistance whereas the other MOSFET has
the OFF state or the relatively high ON resistance, in the state where the
signal of said one pair of sense nodes is amplified by the operations of
the sense amplifier.
13. A semiconductor memory device according to claim 12,
wherein said transmission MOSFET pairs receiving the gate voltage of said
select level are turned ON, and
wherein said transmission MOSFET pairs receiving the gate voltage of said
unselect level are turned OFF.
14. A semiconductor memory device comprising:
a plurality of word lines;
a pair of complementary bit lines;
a plurality of dynamic memory cells individually connected with said
plurality of word lines;
a sense amplifier for amplifying a read signal which is caused to appear on
said pair of complementary bit lines when a memory cell is selected; and
a pair of MOSFETs interposed between a pair of sense nodes of said sense
amplifier and said pair of complementary bit lines, which receives a
control signal at their gates,
wherein said control signal can be selectively set to one of a select
level, an unselect level and intermediate level,
wherein after said read signal has appeared on said pair of complementary
bit lines, said control signal is changed from said select level to the
intermediate level,
wherein after the start of the operation of said sense amplifier, said
control signal is returned from said intermediate level to said select
level, and
wherein at said select level, said pair of MOSFETs are turned ON; at said
unselect level, said pair of MOSFETs are turned OFF; and at said
intermediate level, said pair of MOSFETs are adapted such that they have
an OFF state or a relatively high ON resistance, in the state where said
read signal appears on said pair of complementary bit lines, and such that
one MOSFET of said pair of MOSFETs has an ON state or a relatively low ON
resistance whereas the other MOSFET has the OFF state or the relatively
high ON resistance, in the state where the signal of said one pair of
sense nodes is amplified by the operations of the sense amplifier.
15. A semiconductor memory device according to claim 14,
wherein said sense amplifier includes a CMOS latch circuit for outputting
signals of a high level and a low level to said one pair of sense nodes,
wherein said one MOSFET adapted to have said ON state or said relatively
low ON resistance receives the signal of said low level, and
wherein said other MOSFET adapted to have said OFF state or said relatively
high ON resistance receives the signal of said high level.
16. A semiconductor memory device according to claim 15,
wherein said pair of MOSFETs are of an N-channel type,
wherein said select level is the select level of said word lines,
wherein said unselect level is the low level of the output signal of said
CMOS latch circuit, and
wherein said intermediate level is the high level of the output signal of
said CMOS latch circuit.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor memory device and, mainly,
to a technique which is effective when utilized in a dynamic RAM (Random
Access Memory) including switch MOSFETs between a sense amplifier and bit
lines.
The dynamic RAM, which is intended to raise the speed of the sense
amplifier by turning OFF the selected side of a shared select MOSFET
temporarily to lighten the load on the sense amplifier, has been disclosed
in Japanese Patent Laid-Opens Nos. 64-73596, 5-62463 and 8-106781. In
Japanese Patent Laid-Open No. 4-167293, on the other hand, there is
disclosed a dynamic RAM. In this dynamic RAM, switch MOSFETs which are
interposed between the input/output nodes of the sense amplifier and
complementary bit lines, are first set to the unselect level at the time
of starting the amplification of the sense amplifier, so that the sense
amplifier and the complementary bit lines are isolated to start the
amplifying operations. After a column selection, the gate voltage of the
switch MOSFETs is set to an intermediate potential to perform the
operations in parallel to output one of the sense amplifier amplification
signals to the IO lines and to restore the other amplification signal in
the bit lines. After this, the gate voltage of the switch MOSFETs is
returned to the select level so that the one amplification signal is
re-stored through the bit lines in the memory cells.
Here, the terminlogy "MOS(Metal Oxide Semiconductor)FET" includes a
"MIS(Metal Insulated Semiconducor)FET according to general recognition,
and widely refers to a field effect transistor.
SUMMARY OF THE INVENTION
As in the dynamic RAM disclosed in Japanese Patent Laid-Opens Nos.
64-73596, 5-62463 and 8-106781, before the amplification start of the
sense amplifier, the shared select MOSFETs are turned OFF to isolate the
complementary bit lines and the sense nodes of the sense amplifier. The
sense nodes, even if at a full amplification level state, are lowered at
their level, when the shared select MOSFETs are returned again to the ON
state. By the charge share between the read charge from the memory cells
held in a relatively high parasitic capacity of the bit lines and the
charge in the sense nodes, the potential of the sense nodes drops so that
the signal amplitude is temporarily reduced, as clarified by our
investigations. Alternatively, even when the sense nodes are connected
with the data output lines by the column selecting operation, the signal
amplitude of the sense nodes is also temporarily reduced, as clarified by
our investigations, by the charge share between the precharge charge held
in the parasitic capacity of the data output lines and the charge in the
sense nodes. As a result, in the column selecting operation, the column
selecting operation has to take a relatively long time for transmitting
the signal of the sense nodes to the data input/output lines, and this
long time causes an obstruction to the high speed, as also clarified by
our investigations.
In the Japanese Patent Laid-Open No. 4-167293, the gates of the switch
MOSFETs are set to the intermediate potential to cause the sense amplifier
to effect outputting at the low level to the I/O lines. In parallel with
this, the re-storage (or reloading) of the data is effected in the bit
lines on the high level side. As well known in the art, however, the
memory cells store the binary information. Even if the re-storage of the
data on the high level side is exclusively accelerated, as described
above, the effect in view of the overall memory access is questionable, as
clarified by our investigations, considering that the data re-storage on
the low level side is not performed before the switch MOSFETs are returned
to the ON state. On the 43 other hand, that effect involves a problem in
that the timing control at the level is complicated, as clarified by our
investigations, considering that the gate voltage to be fed to the gate of
one switch MOSFET is changed between the unselect level--the select
level--the intermediate level--the unselect level within a short time
period from just before the start of the sense operation to the restoring
operation of the bit lines so, that the provision of the switch MOSFETs
makes no sense if the transfer from the select level to the intermediate
level is not made before the sense output grows sufficient, and that the
elements have a process dispersion. It has been further clarified by our
investigations that the change from the intermediate level to the unselect
level raises an obstruction to the high speed of the re-storage
operations.
An object of the invention is to provide a semiconductor memory device
which has realized a stable amplifying operation and a high speed in a
sense amplifier with a simple construction. The foregoing and other
objects and novel features of the invention will become apparent from the
description to be made with reference to the accompanying drawings.
Representative aspects of the invention to be disclosed herein will be
briefly summarized in the following. Specifically, switch MOSFETs are
interposed between a sense amplifier disposed in a dynamic RAM and
complementary bit lines. After signal voltages have been read out by the
selecting operations of said word lines, from a plurality of selected
dynamic memory cells, to the plurality of pairs of complementary bit lines
in accordance with their individual storage informations, the switch
control signal of said switch MOSFETs is changed from a select level to
the intermediate potential having: (a) an OFF state or a relatively high
ON resistance for the signal voltage read out to said complementary bit
lines; (b) an ON state with a relatively low ON resistance for a potential
at which the sense nodes are set to one level by the amplifying operation
of the sense amplifier; and (c) an OFF state at a potential of the other
level. The sense amplifier is fed with an operating voltage to start the
amplifying operation in response to the change in said switch control
signal; an amplification signal generated by said amplifying operation is
transmitted through the column select circuit to said input/output lines
in response to the column select signal; and said switch control signal is
returned to the select level in response to the selecting operation of
said column select circuit.
With the construction thus far described, in the amplifying operation of
the sense amplifier, one of the sense nodes is connected with the bit line
so that a high signal charge can be established by the parasitic capacity
on the bit lines. In the column selecting operation, therefore, a high
read signal can be outputted to the data input/output lines thereby to
effect the high speed of the sense output operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic layout diagram showing one embodiment of the dynamic
RAM to which the invention is applied;
FIG. 2 is a schematic layout diagram showing one embodiment of the sub
array and its peripheral circuit in the dynamic RAM according to the
invention;
FIG. 3 is a circuit diagram of one simplified embodiment of the dynamic RAM
according to the invention, showing the area around the sense amplifier
portion thereof from the address input to the data output;
FIG. 4 is a circuit diagram showing one embodiment of the sense amplifier
portion of the, dynamic RAM according to the invention;
FIG. 5 is a circuit diagram showing one embodiment of the main amplifier
shown in the embodiment of FIG. 3;
FIG. 6 is a circuit diagram showing one embodiment of the output buffer of
the dynamic RAM according to the invention;
FIG. 7 is a timing chart for explaining one example of the reading
operation of the dynamic RAM according to the invention;
FIG. 8 is a timing chart for explaining the reading operation of the
dynamic RAM according to the invention;
FIG. 9 is a timing chart for explaining another example of the reading
operation of the dynamic RAM according to the invention;
FIG. 10 is a circuit diagram showing one embodiment of the timing
generation circuit for generating the shared select signal;
FIG. 11 is a timing chart for explaining another example of the reading
operation of the dynamic RAM according to the invention;
FIG. 12 is a circuit diagram showing one embodiment of the sense amplifier
having the overdrive function;
FIG. 13 is a schematic element layout diagram showing one embodiment of the
sense amplifier portion to be used in the dynamic RAM according to the
invention;
FIG. 14 is a timing chart for explaining another example of the reading
operation of the dynamic RAM according to the invention;
FIG. 15 is a circuit diagram showing the sense amplifier portion of another
embodiment of the dynamic RAM according to the invention; and
FIG. 16 is a waveform diagram for explaining the operations when the
invention is applied to a synchronous DRAM.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic layout diagram showing one embodiment of a dynamic
RAM to which the invention is applied. In FIG. 1, of the individual
circuit blocks of the dynamic RAM to which the invention is applied, a
main portion is clearly shown and formed over one semiconductor substrate
of single crystalline silicon by the well-known technique for
manufacturing a semiconductor integrated circuit.
In this embodiment, the memory array is divided into four parts, although
the invention is not especially limited thereto. At a central portion 14
in the longitudinal direction of the semiconductor chip, there are
provided an input/output interface circuit including an address input
circuit, a data input/output circuit and a bonding pad array, a power
supply circuit including a voltage step-down circuit, and so on. On the
two sides, contacting the memory arrays, of the central portion 14, there
are arranged column decoder regions 13.
Each of the four memory arrays, as divided into two left and right arrays
and into two upper and lower arrays with respect to the longitudinal
direction of the semiconductor chip, as described above, is made to form
one memory bank. In each of the memory arrays, a main row decoder region
11 is provided at an up-and-down center portion with respect to the
longitudinal direction. Above and below this main row decoder region,
there are formed main word driver regions 12 which individually drive the
main word lines of the memory array which has been divided into the upper
and lower arrays.
The memory cell array (or sub array) 15 is formed, as shown in an enlarged
view, such that it is surrounded by sense amplifier regions 16 and sub
word driver regions 17. The sense amplifier region and the sub word driver
region provides an intersection region (or cross area) 18 at their
intersecting portion. A sense amplifier, as provided in the sense
amplifier region 16, is constructed by the shared sense method. On the
left and right sides around the sense amplifier other than those arranged
on the two ends of the memory cell array, there are provided complementary
bit lines, which are selectively connected with the complementary bit
lines of the left or right memory cell array.
The memory arrays, as divided into four and right arrays with respect to
the longitudinal direction of the semiconductor chip, as described above,
are arranged in two pairs. At the central portions of the two memory
arrays thus arranged in the pairs, there are arranged the main row decoder
region 11 and main word drivers 12. These main word drivers 12 generate a
select signal for selecting main word lines, which are extended through
one of the memory arrays. On the other hand, the main word drivers 12 are
provided with sub word selecting drivers, which are extended in parallel
with the main word lines to generate a sub word selecting line signal, as
will be described hereinafter.
One memory cell array (or sub array) 15 as shown in the enlarged view, is
provided with 256 sub word lines, although not shown, and 256 pairs of
complementary bit lines (or data lines) perpendicular to the former,
although the invention is not especially limited thereto. Alternatively,
there are provided 512 sub word lines and 512 pairs of complementary bit
lines perpendicular to the former. If the one memory array is provided, as
shown, with sixteen memory cell arrays (or sub arrays) 15 in the bit line
direction, the sub word lines are provided as a whole about 4 K for the
256 construction and about 8 K for the 512 construction. Since eight
memory cell arrays are provided in the word line direction, the
complementary bit lines are provided as a whole about 4 K for the 256
construction and 8 K for the 512 construction. Since these eight memory
arrays are provided as a whole, the overall storage capacity is
8.times.2K.times.4K=64M bits or 8.times.4K.times.8K=256 Mbits.
The one memory array is divided into eight with respect to the main word
line direction. For each memory cell array 15 thus divided, there is
provided a sub word driver (or sub word line driver) 17. This sub word
driver 17 is divided to have one eighth of the length of the main word
lines to generate a select signal for selecting the sub word lines
extending in parallel with the former. In this embodiment, in order to
reduce the number of main word lines, i.e., in order to widen the wiring
pitch of the main word lines, four sub word lines are arranged with
respect to one main word line in the complementary bit line direction,
although the invention is not especially limited thereto. A sub word
selecting driver is arranged to select one of the sub word lines which are
thus divided into eight in the main word line direction and assigned every
four in the complementary bit line direction. The sub word selecting
driver generates a select signal for selecting one of the four sub word
selecting lines extending in the array direction of the sub word drivers.
As described above, one memory array has the storage capacity of 4 Kbits or
8 Kbits with respect to the complementary bit line direction. If the
memory cells as high as 4 K or 8K are connected with one complementary bit
line, however, the parasitic capacity of the complementary bit lines
increases so that a signal level to be read cannot be obtained due to the
small capacity ratio to an information storing capacitor. Therefore, the
division is also made into sixteen with respect to the complementary bit
line direction. Specifically, the complementary bit lines are divided into
sixteen by the sense amplifiers 16, as indicated by thick black lines.
Although the invention is not especially limited thereto, the sense
amplifier 16 is constructed by the shared sense method, and the
complementary bit lines are provided on the left and right of the sense
amplifier 16 except for those which are arranged at the two ends of the
memory array, so that the sense amplifier 16 is selectively connected with
either the left or right complementary bit lines.
In order to retain the signal amount to be read out to the bit lines, the
sub array may be constructed such that the number of memory cells to be
connected therewith is set to 256 (excepting the redundancy cells) to make
the number of divisions of bit lines more than that of word lines (or sub
word lines). In the dynamic RAM of this case having a storage capacity of
about 256 Mbits, each of quartered memory arrays has a storage capacity of
8K.times.8K=64 Mbits. As a result, the bit lines are divided into thirty
two whereas the word lines are divided into sixteen, and the sub arrays
are correspondingly provided.
FIG. 2 is a schematic layout diagram showing one embodiment of the sub
array and its peripheral circuit in the dynamic RAM according to the
invention. In FIG. 3, the regions to have sub arrays SBARY are
discriminated by hatching them from the sub word driver regions, the sense
amplifier regions and the cross areas, as provided in the peripheries of
the former.
The sub array SBARY is divided into the following four kinds in the example
of the construction of 256.times.256. If the extending direction of the
word lines is horizontal, more specifically, the first sub array SBARY, as
located at the righthand lower position, is arranged with 256 sub word
lines SWL, and the complementary bit lines are made up of 256 pairs.
Therefore, 256 sub word drivers SWD corresponding to the 256 sub word
lines SWL are divided into halves of 128 and arranged on the left and
right sides of that sub array. In addition to the shared sense amplifier
construction, 256 sense amplifiers SA, as provided to correspond to the
256 pairs of complementary bit lines BL, are alternately arranged by 128
above and below that sub array.
The second sub array SBARY, as located at the righthand upper position, is
provided with eight preparatory (or redundancy) word lines in addition to
the 256 normal sub word lines SWL, although the invention is not
especially limited thereto, and the complementary bit lines are composed
of 256 pairs. Therefore, the 264 sub word drivers SWD corresponding to the
(256+8) sub word lines SWL are separately arranged with 132 on the left
and right of that sub array. Like the above, the 128 sense amplifiers are
arranged above and below. Specifically, the 128 pairs of complementary bit
lines of the 256 pairs, as formed in the sub arrays SBARY arranged above
and below on the right side, are commonly connected through a shared
switch MOSFET with the sense amplifier SA interposed inbetween.
The third sub array SBARY, as located at the lefthand lower position, is
constructed to have 256 sub word lines SWL as in the adjoining righthand
sub array SBARY. Like above, the 128 sub word drivers are separately
arranged. The 128 of the 256 sub word lines SWL of the sub arrays SBARY,
as located at the lefthand and righthand lower positions, are commonly
connected with the 128 sub word drivers SWD which are formed in the
regions interposed inbetween. As described above, the sub array SBARY, as
located at the lefthand lower position, is provided with four pairs of
preparatory (or redundancy) bit lines 4RED in addition to the 256 pairs of
normal complementary bit lines BL. Therefore, the 260 sense amplifiers SA
corresponding to the 260 pairs of complementary bit lines BL are
separately arranged with 130 above and below that sub array.
The fourth sub array SBARY, as located at the lefthand upper position, is
provided, as in the adjoining righthand sub array SBARY, with 256 normal
sub word lines SWL and eight preparatory sub word lines and, as in the
adjoining lower sub array, with four pairs of preparatory bit lines in
addition to 256 pairs of normal complementary bit lines. Therefore, the
sub word drivers are separately arranged with 132 on the left and right
sides, and the sense amplifiers SA are separately arranged with 130 above
and below.
The main word lines MWL are so extended in the horizontal direction that
one of them is exemplified. On the other hand, column selecting lines YS
are so extended in the vertical direction that one of them is exemplified.
The sub word lines SWL are arranged in parallel with the main word lines
MWL, and the (not-shown) complementary bit lines BL are arranged in
parallel with the column selecting lines YS.
For the four sub arrays, eight sub word selecting lines FX0B to FX7B are
extended like the main word lines MWL through the four sets of (or eight)
sub arrays. Moreover, the four sub word selecting lines FX0B to FX3B and
the four sub word selecting lines FX4B to FX7B are extended separately
over the upper and lower sub arrays. The reason why one set of sub word
selecting lines FX0B to FX7B are thus assigned to the two sub arrays and
extended over the sub arrays is to reduce the memory chip size.
Specifically, when the eight sub word selecting lines FX0B to FX7B are
assigned to each sub array and are formed in the wiring channels over the
sense amplifier area, the number of wiring channels necessary is as much
as 8.times.32=256 for the 32 sense amplifiers in the shorter side
direction, as in the memory array of FIG. 1. In the foregoing embodiment,
on the contrary, the wiring lines can be formed without any special
dedicated regions by assigning the eight sub word selecting lines FX0B to
FX7B commonly to the two upper and lower sub arrays and by arranging them
over the sub arrays in parallel with the main word lines and in a mixed
manner.
Intrinsically, one main word line is provided over the sub array for eight
sub word lines, and the sub word selecting lines are demanded for
selecting one of the eight sub word lines. Since one main word line MWL is
formed for the eight sub word lines SWL which are formed according to the
pitch of the memory cells, the main word lines MWL have a wide wiring
pitch. It is, therefore, relatively easily effected by sacrificing the
width of the wiring pitch slightly to form the sub word selecting lines
between the main word lines MWL by making use of the same wiring layer as
that of the main word lines MWL.
The sub word driver SWD of this embodiment adopts a construction to select
one sub word line SWL by using a select signal, as fed through the sub
word selecting lines FX0B and so on, and a select signal inverted from the
former. Moreover, the sub word driver SWD adopts a construction to select
the sub word lines SWL of the sub arrays arranged on its left and right
sides. For the two sub arrays sharing the FX0B, therefore, the four sub
word selecting lines are shared and fed to as many as 128.times.2=256 sub
word drives. In other words, noting the sub word selecting line FX0B, for
the two sub arrays, the select signal has to be fed to as many as
256.div.4=64 sub word drives SWD.
If the first sub word selecting line FX0B is extended in parallel with the
main word line MWL, there is provided a second sub word selecting line FX0
which is provided in the lefthand upper cross area, to feed the select
signal to the sixty four sub word drivers arrayed on the upper and lower
sides through the sub word selecting line driver FXD for receiving the
select signal from the first sub word selecting line FX0B. This first sub
word selecting line FX0B is extended in parallel with the main word lines
MWL and the sub word lines SWL, whereas the second sub word selecting line
is extended over the sub word driver region in parallel with the column
selecting lines YS and the complementary bit lines BL perpendicular to the
first sub word selecting line FX0B. Like the eight first sub word
selecting lines FX0B to FX7B, the second sub word selecting lines FX0 to
FX7 are divided into even lines FX0, 2, 4 and 6 and odd lines FX1, 3, 5
and 7 and are separately arranged in the sub word drivers SWD disposed on
the left and right sides of the sub array SBARY.
The sub word selecting line drivers FXD are separately arranged with two
above and below-one cross area, as indicated by solid squares in FIG. 2.
In the lefthand upper cross area, more specifically: the sub word
selecting line driver arranged on the lower side corresponds to the first
sub word selecting line FX0B; the two sub word selecting line drivers FXD
disposed in the lefthand intermediate cross area correspond to the first
sub word selecting line FX2B and FX4B; and the sub word selecting line
driver arranged on the upper side of the lefthand lower cross area
corresponds to the first sub word selecting line, FX6B.
In the center upper cross area: the sub word selecting line driver arranged
on the lower side corresponds to the first sub word selecting line FX1B;
the two sub word selecting line drivers FXD disposed in the center
intermediate cross area correspond to the first sub word selecting line
FX3B and FX5B; and the sub word selecting line driver arranged on the
upper side of the center lower cross area corresponds to the first sub
word selecting line FX7B. In the righthand upper cross area, moreover, the
sub word selecting line driver arranged on the lower side corresponds to
the first sub word selecting line FX0B; the two sub word selecting line
drivers FXD disposed in the righthand intermediate cross area correspond
to the first sub word selecting line FX2B and FX4B; and the sub word
selecting line driver arranged on the upper side of the righthand lower
cross area corresponds to the first sub word selecting line FX6B. In the
sub word drivers thus disposed at the end portions of the memory array, no
sub array is present on their right side so that the sub word lines SWL on
the left side are exclusively driven.
With the construction of this embodiment in which the sub word selecting
lines FXB are arranged between the gaps of the pitches of the main word
lines MWL over the sub arrays, no special wiring channel can be demanded
so that the memory chip is not enlarged even if the eight sub word
selecting lines are arranged for each sub array. With the sub word
selecting line driver FXD being formed, however, the cross areas are
enlarged to obstruct the higher integration. In these cross areas, more
specifically, there is no areal margin for forming peripheral circuits
such as a switch circuit IOSW provided to correspond to main input/output
lines MIO or local input/output lines LIO, as indicated by dotted lines in
FIG. 2, power MOSFETs for driving the sense amplifiers, drivers for
driving the shared switch MOSFETs, or drivers for driving the precharge
MOSFETs. In an embodiment of FIG. 3, therefore, the two upper/lower sub
arrays share the sub word selecting line driver FXD to prevent the areal
increase.
Of the cross areas, the one arranged in an extending direction A of the
second even sub word selecting lines FX0 to FX6 is provided with: an
N-channel power MOSFET Q15 for feeding an internal constant voltage VDL to
the sense amplifiers (and an N-channel power MOSFET Q16 for feeding a
power voltage VDD for an overdrive), as will be described hereinafter; and
an N-channel power MOSFET Q14 for feeding an earth potential VSS of the
circuit to the sense amplifiers.
Of the cross areas, the one arranged in the extending direction B of the
second odd sub word selecting lines FX1 to FX7 is provided with: an
inverter circuit for turning OFF a MOSFET for precharging and equalizing
the bit lines; and an N-channel power MOSFET for feeding the earth
potential VSS of the circuit to the sense amplifiers, although the
invention is not especially limited thereto. This N-channel power MOSFET
feeds the earth potential to a common source line (CSN) of MOSFETs for
amplifying the N-channel MOSFET, constructing the sense amplifiers from
the two sides of the sense amplifier array. To the 128 or 130 sense
amplifiers belonging to the sense amplifier area, more specifically, there
is fed the earth potential from both the N-channel power MOSFETs disposed
in the A-side cross area and the N-Channel power MOSFETs disposed in the
B-side cross area.
As described above, the sub word line driver SWD selects the sub word lines
of the sub arrays on its two left and right sides. On the other hand, the
two left and right sense amplifiers are activated to correspond to the sub
word lines of the two sub arrays selected. When the sub word lines are
brought into the selected state, more specifically, the address selecting
MOSFETs are turned ON so that the charge of the storage capacitor is
synthesized with the bit line charge. It is, therefore, necessary to
perform the reloading operation to activate the sense amplifiers to
restore the initial charge state. Excepting those corresponding to the sub
arrays at the end portions, therefore, the power MOSFETs are used to
activate the sense amplifiers on their two sides. In the sub word line
driver SWD disposed on the right or left side of the sub arrays at the
ends of their group, on the contrary, only the sub word lines of the sub
arrays are selected so that the power MOSFETs activate only the sense
amplifier group on one side corresponding to the sub arrays.
The sense amplifiers are made to have the shared sense construction. In the
sub arrays arranged on the two sides across the sense amplifiers, these
sense amplifiers perform the reloading operation to amplify the read
signals of the complementary bit lines corresponding to the selected sub
word lines by turning OFF to isolate the shared switch MOSFETs
corresponding to the complementary bit lines on the side of the
non-selected sub word lines, and to return the storage capacitors of the
memory cells to the initial charge state. In this case of the embodiment,
the shared switch MOSFETs of the complementary bit lines corresponding to
the selected sub word lines are lowered to an intermediate potential in
response to the amplifying operations of the sense amplifiers and are
returned again to the select level after the read signals from the memory
cells were amplified and transmitted to the input/output lines through
column select circuits.
FIG. 3 shows a circuit diagram of one simplified embodiment of the dynamic
RAM according to the invention around the sense amplifier portion thereof
from the address input to the data output. In FIG. 3, the sense amplifier
16, as vertically sandwiched between the two sub arrays 15, and the
circuit of the cross area 18 are exemplified, but the others are shown in
block form. On the other hand, the circuit blocks indicated by dotted
lines are individually designated by the reference characters.
One of the dynamic memory cells, which is interposed between the sub word
line SWL for said one sub array 15 and one line BLT of the complementary
bit lines BLT and BLB, is exemplified as a representative cell. The
dynamic memory cell is constructed to include an address selecting MOSFET
Qm and a storage capacitor Cs. Here, the letter T of the bit line BLT
indicates the true side on which the high level corresponds to the logic
1, and the letter B of the bit line BLB indicates the bar side on which
the low level corresponds to the logic 1.
The address selecting MOSFET Qm has a gate connected with the sub word line
SWL, a drain connected with the bit line BL, and a source connected with
the storage capacitor Cs. The other electrodes of the storage capacitors
Cs are commonly fed with a plate voltage VPLT. A negative back bias
voltage VBB is applied to the substrate (or channel) of the MOSFET Qm. The
select level of the sub word line SWL is set to a high voltage VPP which
is raised by a threshold voltage of the address selecting MOSFET Qm from
the high level of the bit lines.
When the sense amplifier is operated with the internal dropped voltage VDL,
the high level to be amplified by the sense amplifier and fed to the bit
line is set to the level of the internal voltage VDL. Therefore, the high
voltage VPP corresponding to the select level of the word lines is
VDL+Vth+.alpha.. The paired complementary bit lines BLT and BLB of the sub
array disposed on the left side of the sense amplifier are arranged in
parallel, as shown in FIG. 3, and are suitably intersected, if necessary,
so as to balance the capacities of the bit lines. These complementary bit
lines BLT and BLB are connected with the input/output nodes of the unit
circuit of the sense amplifier through shared switch MOSFETs Q1 and Q2.
The unit circuit of the sense amplifier is constructed to include:
N-channel amplify MOSFETs Q5 and Q6 and P-channel amplify MOSFETs Q7 and
Q8 having gates and drains cross-connected into a latch shape. The sources
of the N-channel MOSFETs Q5 and Q6 are connected with the common source
CSN. The sources of the P-channel MOSFETs Q7 and Q8 are connected with a
common source line CSP. The power switch MOSFETs are individually
connected with the common source lines CSN and CSP. Although the invention
is not especially limited, the common source line CSN, with which the
sources of the N-channel amplify MOSFETs Q5 and Q6 are connected, is
supplied with an operating voltage corresponding to the earth potential by
the N-channel power switch MOSFET Q14 disposed in the cross area 18. The
common source line CSP connected with the sources of the P-channel amplify
MOSFETs Q7 and Q8 is provided with the N-channel power MOSFET Q15 disposed
in the cross area 18 for feeding the internal voltage VDL.
Sense amplifier activation signals SAN and, SAP1 to be fed to the gates of
the N-channel power MOSFETs Q14 and Q15 are signals in phase, and the
select level of the signal SAN is set to a relatively low potential such
as the VDL whereas the signal SAP1 uses the power voltage VDD (or the
boosted voltage VPP corresponding to the select level of the word lines,
if necessary) for outputting the operating voltage, e.g., VDL from the
MOSFET Q15.
A sense node or the input/output node of the unit circuit of the sense
amplifier is provided with a precharge circuit, which is constructed to
include an equalize MOSFET Q11 for shorting the complementary bit lines,
and switch MOSFETs Q9 and Q10 for feeding a half precharge voltage VBLR to
the complementary bit lines. The gates of these MOSFETs Q9 to Q11 are
commonly supplied with a precharge signal PCB. The driver circuit for
generating the precharge signal PCB is provided in the cross area with an
inverter circuit, although not shown, for raising the falling speed
thereof. At the starting time of the memory access, more specifically,
prior to the word line selecting timing, the MOSFETs Q9 to Q11 which form
the precharge circuit are quickly switched through the inverter circuits
which are dispersedly disposed in the individual cross areas.
In addition to the circuits shown in FIG. 3, there are provided, if
necessary, in the cross area 18 a half precharge circuit for setting the
common source lines CSP and CSN of the sense amplifier at an inactive time
to a half precharge voltage (VDL/2), a half precharge circuit for local
input/output lines LIOT and LIOB, a disperse driver circuit for shared
select signal lines SHR and SHL, and so on.
The unit circuit of the sense amplifier is connected through shared switch
MOSFETs Q3 and Q4 with the similar complementary bit lines BLT and BLB of
the sub array 15 on the lower side of the drawing. Switch MOSFETs Q12 and
Q13 form a column switch circuit, which is turned ON when the select
signal YS is set to the select level (or high level), to the sense nodes
or the input/output nodes of the unit circuit of the sense amplifier with
local input/output lines LIO1T, LIO1B, LIO2T and LIO2B. When the sub word
line SWL of the sub array on the upper side is selected, for example, the
shared switch MOSFETs Q1 and Q2 on the upper side of the sense amplifier
are left ON whereas the shared switch MOSFETs Q3 and Q4 on the lower side
are turned OFF.
As a result, the input/output nodes of the sense amplifier are connected
with the upper side complementary bit lines BLT and BLB, to amplify the
minute signal of the memory cell connected with the selected sub word line
SWL thereby to transmit the amplified signal through the column switch
circuit (Q12 and Q13) to the local input/output lines LIO1T and LIO1B.
These local input/output lines LIO1T and LIO1B are connected through the
switch circuit IOSW, which is disposed in the cross area 18 and composed
of N-channel MOSFETs Q19 and Q20, with main input/output lines MIOT and
MIOB connected with the input terminal of a main amplifier 61. Although
not shown, the speed can be raised higher by using a so-called "analog
gate", in which a P-channel MOSFET is provided in parallel with the
MOSFETs Q19 and Q20. By using the power voltage VDD in place of a dropped
voltage VPERI as the gate voltage of the MOSFETs Q19 and Q20, on the other
hand, the ON resistance can be lowered to raise the speed. With the main
input/output lines MIOT and MIOB, on the other hand, there are connected
the output terminals of a write amplifier, although not shown.
Although the invention is not especially limited thereto, in response to
one select signal YS, the column switch circuit connects the two pairs of
complementary bit lines BLT and BLB with the two pairs of local
input/output lines LIO1T and LIO1B, and LIO2T and LIO2B. In the sub array
selected by the selecting operation of one main word line, therefore, a
total of four pairs of complementary bit lines are selected by the two
pairs of the column switch circuit, which are provided to correspond to
one pair of sense amplifiers on the two sides, so that 4 bits can be
simultaneously read/written by selecting one signal YS.
An address signal Ai is fed to an address buffer 51. This address buffer
operates in a timing sharing manner to fetch an X address signal and a Y
address signal. The X address signal is fed to a predecoder 52 so that the
select signal of the main word line MWL is generated through the main row
decoder 11 and the main word driver 12. The address buffer 51. receives
the address signal Ai fed from the external terminal, so that it is
operated with the power voltage VDD fed from the external terminal, and
the predecoder is operated with the dropped voltage VPERI, whereas the
main word driver 12 is operated with the boosted voltage VPP. A column
decoder (or driver) 53 generates the column select signal YS in response
to the Y address signal which is fed by the time sharing operation of the
address buffer 51.
The main amplifier 61 is operated with the dropped voltage VPERI so that
its signal is outputted from an external terminal Dout (or DQ) through an
output buffer 62, which is operated with the power voltage VDD fed from
the external terminal. A write signal, as inputted from an external
terminal Din (or DQ), is fetched through an input buffer 63 and is fed to
the main input/output lines MIOT and MIOB through a later-described write
amplifier, which contained in the main amplifier 61, as shown. The output
buffer is provided at its input portion with a level shift circuit, as
will be described in the following, and a logic unit for outputting the
signal having a shifted level, in synchronism with the timing signal.
Although the invention is not especially limited thereto, the power voltage
VDD fed from the external terminal is set to 2.5 V, and both the dropped
voltage VPERI fed to the internal circuit and the operating voltage VDL of
the sense amplifier are set to 1.8 V. In this case, these voltages are
generated, although at the same level, by power circuits (or voltage
step-down circuits) independent of each other, so that the power noise due
to the operations of the peripheral circuits may not affect the amplifying
operation of the sense amplifier. The boosted voltage VPP to be used for
the select signal and the unselect signal of the word lines (or sub word
lines or main word lines) are set to 3.5 V. The precharge voltage VBLR of
the bit lines is set to 0.9 V equal to VDL/2, and the plate voltage VPLT
is also set to 0.9 V. Moreover, the substrate voltage VBB is set to -1.0
V.
FIG. 4 is a circuit diagram showing one embodiment of the sense amplifier
portion of the dynamic RAM according to the invention. The circuit of FIG.
4 is basically identical to that shown in FIG. 3. A CMOS latch circuit
constructing a unit circuit of the sense amplifier is constructed to
include the N-channel MOSFETs Q5 and Q6 and the P-channel MOSFETs Q7 and
Q8, as formed in a latch shape. The sources of these N-channel MOSFETs Q5
and Q6 and the P-channel MOSFETs Q7 and Q8 in the latch shape are
connected with the common source lines CSN and CSP which are commonly
commected with the sources of N-channel MOSFETs and P-channel MOSFETs
constructing another not-shown similar sense amplifier, as disposed to
correspond to the same sub array.
An operating voltage VSSA is fed to the common source line CSN through the
N-channel MOSFET Q14 for receiving the timing signal SAN, and the
operating voltage VDL is fed to the common source line CSP through the
N-channel MOSFET Q15 for receiving the timing signal SAP1. In this
embodiment, the earth potential VSSA used as one operating voltage of the
sense amplifier is fed with the earth potential fed from the external
terminal by the earth line separated from that earth potential VSS, so as
to receive no influence of noises from the peripheral circuits or the
like. In short, the earth potential VSSA fed to the sense amplifier is fed
with the earth potential of the circuit directly from the external
terminal through the wiring line which is provided separately from the
peripheral circuits or the input/output circuits.
At a pair of input/output nodes (or sense nodes) SAT and SAB of the latch
circuit, there is provided the precharge circuit which is constructed to
include the equalize MOSFET Q12 for shorting those input/output nodes, and
the precharge MOSFETs Q10 and Q11 for transmitting the half precharge
voltage VBLR to the sense nodes SAT and SAB. On the other hand, the sense
nodes SAT and SAB are connected with the local input/output lines LIOT and
LIOB through the column switch MOSFETs Q12 and Q13 having gates fed with
the column select signal YS. Moreover, the shared switch MOSFETs Q1 and Q2
are provided between complementary bit lines BLLT and BLLB disposed on the
left side across the sense amplifier portion, and the shared switch
MOSFETs Q3 and Q4 are provided between the complementary bit lines BLRT
and BLRB disposed on the right side.
The control signal SHL is fed to the gates of the shared switch MOSFETs Q1
and Q2, and the control signal SHR is fed to the gates of the shared
switches Q3 and Q4. At each of the intersections between the complementary
bit lines BLLT and BLLB on the left side of the sense amplifier portion
and the sub word lines SWL1, SWL2 and so on arranged to intersect the
former at a right angle, there is disposed the dynamic memory cell which
is constructed to include the address selecting MOSFET Qm and the storage
capacitor Cs, as described hereinbefore. Likewise, at each of the
intersections between the complementary bit lines BLRT and BLRB on the
right side of the sense amplifier portion and the sub word lines SWL3,
SWL4 and so on arranged to intersect the former at a right angle, there is
disposed the dynamic memory cell which is constructed to include the
address selecting MOSFET Qm and the storage capacitor Cs, as described
hereinbefore.
FIG. 5 is a circuit diagram showing one embodiment of the main amplifier
shown in the embodiment of FIG. 3. The main amplifier is constructed to
include: a CMOS latch circuit having N-channel MOSFETs Q21 and Q22 and
P-channel MOSFETs Q24 and Q25 in the latch shape as in the sense
amplifier; and an N-channel MOSFET Q23 connected between the commonly
connected sources of the N-channel MOSFETs Q21 and Q22 and the earth
potential of the circuit. The input/output nodes of the CMOS latch circuit
are connected with the main input/output lines MIOT and MIOB, as described
hereinbefore. The commonly connected sources of the P-channel MOSFETs Q24
and Q25 in the latch shape are fed with the operating voltage VPERI. This
voltage VPERI is set at the same voltage as the operating voltage VDL of
the sense amplifier.
Although the invention is not especially limited thereto, the main
input/output lines MIOT and MIOB are precharged together with the local
input/output lines LIOT and LIOB to VPERI (VDL) by the not-shown precharge
circuit disposed on those local input/output LIOT and LIOB. On the output
signals read out to the local input/output lines LIOT and LIOB and the
main input/output lines MIOT and MIOB by the amplifying operations of the
sense amplifier, therefore, one of the main input/output lines MIOT and
MIOB changes from the precharge potential (VPERI=VDL) to a voltage dropped
to the low level side, and the MOSFET Q23 is turned ON with the timing
signal MAE so that the potential difference is amplified by the N-channel
MOSFETs Q21 and Q22 in the latch shape.
FIG. 6 is a circuit diagram showing one embodiment of the output buffer of
the dynamic RAM according to the invention. In FIG. 6, there is also shown
a circuit block which shows the entire operations of the dynamic RAM.
Specifically, the decoder is operated with the dropped voltage VPERI to
generate a decoded signal having a corresponding signal amplitude. The
main word driver is operated with the boosted voltage VPP. The memory
array outputs the read signal having a signal amplitude corresponding to
the operating voltage VDL of the sense amplifier, as described
hereinbefore. The main amplifier is operated with the dropped voltage
VPERI to generate a corresponding read signal MOB. Here, the letter B of
the MOB indicates that the logic "1" is at the low level whereas the logic
"0" is at the light level, and the inverted signal is designated by the
MOT.
In the output buffer, the output signal MOB of the main amplifier converts
(or amplifies) the signal level corresponding to the dropped voltage VPERI
to a voltage level corresponding to the external power voltage VDD by a
level shift circuit LS. This amplified signal MOTH is fed to one input of
a NAND gate circuit G1. On the other hand, the signal MOTH is inverted by
an inverter circuit N1 and fed to one input of a NAND gate circuit G2. The
other inputs of these NAND gate circuits G1 and G2 are supplied with a
data output timing signal DOC at a signal level corresponding to the power
voltage VDD. Output MOSFETs QP and QN have large gate capacities because
they are formed to have relatively large sizes for achieving high load
driving abilities. In order to drive those output MOSFETs QP and QN at a
high speed, the output signals of the gate circuits G1 and G2 are
sequentially transmitted through inverter circuits N2 to N4.
The power voltage VDD to be fed to the source of the P-channel output
MOSFET QP of the output buffer is fed through an independent power
terminal VDDQ and the power line with the operation voltage so that the
P-channel output MOSFET QP may cause flow a relatively high operating
current to flow. Likewise, the earth potential to be applied to the source
of the P-channel output MOSFET QN is fed through an independent earth
terminal VSSQ and the power line. The P-channel output MOSFET QP can be
replaced by an N-channel output MOSFET. In order to achieve the output
level up to the power voltage VDD, however, a boosted voltage may be fed
to the gate. This boosted voltage may utilize the boosted voltage VPP of
the word line or the like but is generally generated by a bootstrap
circuit.
FIG. 7 is a timing chart for explaining one example of the reading
operation of the dynamic RAM according to the invention. The shared select
signals SHR and SHL are set for the precharge period to the select level
such as the boosted voltage VPP. By the precharge circuit disposed at the
sense node of the sense amplifier, therefore, the complementary bit lines
BLLT and BLLB and so on, as disposed on the left and right sides of the
precharge circuit, are set to a half precharge voltage VBLR (=VDL/2).
Before the sub word line SWL1 is selected, the shared select signal SHR
corresponding to the sub array on the unselected side is set to an
unselect level such as the earth potential VSS of the circuit. Therefore,
the sense amplifier is isolated from the complementary bit line on the
right side so that a minute voltage difference corresponding to the stored
charge of the selected memory cell is generated on the complementary bit
lines BLLT and BLLB on the left side by the selecting operations of the
sub word line SWL1.
Before the minute voltage is generated so that the sense amplifier starts
its amplifying operation, the shared select signal SHL is dropped to an
intermediate voltage such as the dropped voltage VDL. Then, the sense
amplifier activation signals SAN and SAP1 are raised to the high level to
start the amplifying operation of the sense amplifier. Specifically, the
power switch MOSFET Q14 is turned ON with the sense amplifier activation
signal SAN to drop the common source line CSN of the sense amplifier from
the half precharge voltage to a potential such as the earth potential VSSA
of the circuit, and the power switch MOSFET Q15 is turned ON with the
sense amplifier activation signal SAP1 to raise the common source line CSP
of the sense amplifier from the half precharge voltage to the operating
voltage VDL.
In this amplifying operation, as shown in the enlarged diagram, the
potential of the shared select signal SHL on the selected side drops to a
low potential such as VDL, and the switch MOSFETs Q1 and Q2 connect the
bit lines BLLT and BLLB with a relatively large ON resistance because the
potential between the sense nodes SAT and SAB is as small as about 0.9 V.
Therefore, a high parasitic capacity of the bit lines BLLT and BLLB is not
directly connected with the sense nodes SAT and SAB so that the sense
nodes SAT and SAB are quickly extended in a manner to correspond to the
minute potential difference by the amplification start of the sense
amplifier.
Specifically, the sense node SAT corresponding to the read signal at the
high level quickly rises to the VDL because the switch MOSFET Q1 is OFF.
In the sense node SAB corresponding to the read signal at the low level,
on the other hand, the potential between the gate and the source of the
switch MOSFET Q2 is extended in response to the drop of the potential to
strengthen the coupling to the bit line BLLB thereby to drop the potential
of the bit line BLLB.
At the time of starting the amplification of the sense amplifier, more
specifically, the switch MOSFET Q1 is turned OFF, and the switch MOSFET Q2
is turned ON with a large resistance, to provide a coarse coupling between
the sense node and the bit lines BLLT and BLLB. As a result, the minute
potential difference is quickly enlarged by the amplifying operation of
the sense amplifier, and the switch MOSFET Q2 on the low level side
densities the coupling to the bit line BLLB in a manner to correspond to
the extension of the amplification voltage thereby to promote the drop of
the potential of the bit line BLLB. In other words, the switch MOSFET Q2
at this time functions as the so-called "linear amplification MOSFET Q2"
having a grounded gate and a source input thereby to drop the potential of
the bit line BLB.
The sense amplifier performs high-speed operations utilizing the positive
feedback loop with the minute voltage to be transmitted to the sense nodes
SAT and SAB. If noises rise at the amplification starting time to invert
the potential difference with respect to the read level, an erroneous
reading operation is caused, that is, the amplified output is reloaded in
the memory cells to cause an erroneous storing operation. At the
amplification starting time of the sense amplifier, therefore, the
coupling to the bit lines is coarse because the gate-source voltage is in
the vicinity of a threshold voltage, even if the shared switch MOSFETs Q1
and Q2 are ON. Therefore, the minute potential difference is quickly
enlarged while preventing the influences of noises from the bit line side.
In response to this enlargement, the switch MOSFET Q1 on the high level
side is turned OFF, and the ON resistance of the switch MOSFET Q2 is
gradually reduced in response to the enlargement of the amplification
signal to the low level side, so that the potential is lowered by
densifying the coupling to the bit lines when the amplifying operation is
performed quickly and stably.
Thus, the sense node SAB is given a substantially high signal charge by the
connection with the bit line BLLB having a relatively high parasitic
capacity through the switch MOSFET Q2. When the sense node SAB is
connected with the local bit line in response to the column select signal
YS, therefore, the signal amount to be read out by the charge share with
the local bit line can be increased to effect a fast reading.
FIG. 8 is a timing chart for explaining the reading operation of the
dynamic RAM according to the invention. This timing chart is intended to
explain the superiority of the reading operation at the intermediate
potential in accordance with the invention, by comparing the reading
operation of the prior art, in which the shared switch MOSFET on the
selected side is completely turned OFF.
When the sense amplifier is activated by setting the shared select signal
SHL to the low level such as the earth potential VSSA of the circuit, as
shown in FIG. 8, the potentials of the sense nodes SAT and SAB abruptly
enlarge their minute reading potential difference. When the shared select
signal SHL is returned to the select level, however, the sense nodes SAT
and SAB are shifted to the bit line potential side by the charge share
between the bit lines BLT and BLB having the relatively high parasitic
capacity so that their potential difference becomes as small as V2. When
the column select signal YS is set to the high level at this timing and
connected with the local input/output lines for the reading operation, the
signal amount to be transmitted through the local input/output lines to
the main input/output lines MIOT and MIOB is delayed to reach a voltage V3
necessary for the amplifying operation of the main amplifier connected
therewith. Therefore, the column select signal YS is set at the select
level until the voltage level V3 is achieved, so that connection between
the sense nodes and the local input/output lines has to be maintained.
On the contrary, when the shared select signal SHL on the selected side is
dropped to the intermediate potential VDL, as indicated by dotted lines,
as in the invention, the potential of the bit line BLB has been dropped
even if the shared select signal SHL is returned to the select level,
because the amplified output on the low level side is transmitted to the
bit line BLB for the amplification period of the sense amplifier. As a
result, the potential difference between the sense nodes SAT and SAB is
enlarged as indicated by V1. When the column select signal YS is raised to
the high level to effect the reading operation with the connection being
made with the local input/output lines, therefore, the signal amount to be
transmitted through the local input/output lines to the main input/output
lines MIOT and MIOB can be increased, as indicated by dotted lines in FIG.
8, so that the time period to reach the voltage level V3 necessary for the
amplifying operation of the main amplifier connected therewith can be
shortened. In accordance with this, an activation signal MAE of the main
amplifier can be timed earlier, and the select period of the column select
signal YS can be shortened.
The intermediate voltage should not be limited to the operating voltage VDL
of the sense amplifier. This intermediate potential may be ideally within
VT2<Intermediate Potential<VT1, if the threshold voltages of the MOSFETs
Q1 and Q2 are designated by VT1 and VT2. Even with another range of VT1,
VT2<Intermediate Potential, however, there arises no problem so long as
the ON resistance is so high as to exert no substantial influence upon the
start of amplification of the sense amplifier.
The threshold voltages VT1 and VT2 are expressed by the following formulas
(1) and (2):
VT1=VT10+K.vertline.VBB-VSAT.vertline.+2.PHI.F-2.PHI.F (1)
and
VT2=VT20+K.vertline.VBB-VSAB.vertline.+2.PHI.F-2.PHI.F (2).
Here: VT10 a threshold voltage for VBB-VSAT=0; VT20 a threshold voltage for
VBB-VSAB=0; K a substrate effect constant; VSAT a voltage value of the
sense node SAT; VSAB a voltage value of the sense node SAB; VBB a
substrate voltage; and .PHI.F a Felmi-level.
FIG. 9 is a timing chart for explaining another example of the reading
operation of the dynamic RAM according to the invention. In this
embodiment, when the shared select signal SHL on the selected side is set
to the intermediate potential VDL and then is returned to the select
level, such as the voltage VPP, the rising time tr is delayed to tr1. As a
result, the coupling between the bit line BTL and the sense node SAT on
the high level side is made gentle to reduce the drop of the bit line BLT.
As a result, the potential difference between the sense nodes SAT and SAB
can be enlarged from V1 to V5. This makes it possible to read out the
sense output at a high speed to the data input/output lines.
FIG. 10 is a circuit diagram showing one embodiment of the timing
generation circuit for generating the shared select signal. Three timing
signals .o slashed.A, .o slashed.B and .o slashed.C are generated by an SH
select logic block. For example, the timing signals .o slashed.B and .o
slashed.C are generated on the selected side, whereas the timing signals
.o slashed.A and .o slashed.C are generated on the unselected side. On the
selected side, more specifically, the timing signals .o slashed.C, .o
slashed.B and .o slashed.C are generated to turn ON output MOSFETs Q27,
Q26 and Q27 correspondingly, so that the SHL (SHR) potential is set to a
binary voltage of VPP-VDL-VPP. On the unselected side, the timing signals
.o slashed.C, .o slashed.A and .o slashed.C are generated to turn ON
output MOSFETs Q27, Q28 and Q27 correspondingly, so that the SHL (SHR)
potential is set to a binary voltage of VPP-VSS-VPP.
When the select level is set at the VPP level, as described above, the
select level of the timing signal .o slashed.C is set to the boosted
voltage of VPP+VT27 for the MOSFET Q27 made of an N-channel MOSFET. For
the MOSFET Q27 made of a P-channel MOSFET, the timing signal .o slashed.C
has the unselect level of the VPP and select level of VSS.
When the rise from the intermediate voltage VDL to the select level VPP is
to be delayed, as shown in FIG. 9, the MOSFET Q27 may be made of two
MOSFETs connected in parallel to turn ON the two MOSFETs simultaneously
for rise from VSS to the VPP and one of them for rise from VDL to the VPP.
Alternatively, the rise of the timing signal .o slashed.C may be delayed.
By thus changing the size of the MOSFETs and the gate input voltage, it is
possible to make the selective signal level changes.
FIG. 11 is a timing chart for explaining another example of the reading
operation of the dynamic RAM according to the invention. In this
embodiment, the sense amplifier is overdriven. Specifically, the voltage
VDD higher than the operating voltage VDL is fed to the common source line
CSP of the P-channel MOSFETs of the sense amplifier to steepen its rise
thereby to quicken the rise of the sense output on the high level side.
For this, a timing signal SAP2 is added as the timing signal for driving
the common source line CSP. This timing signal SAP2 is temporarily raised
to a high voltage such as the VPP level simultaneously with the timing
signal SAN thereby to make the common source line CSP temporarily higher
than VDL. In response to the change of this timing signal SAP2 to the
unselect level, the timing signal SAP1 is generated with a delay to feed
the common source line CSP with the operating voltage VDL.
By this overdrive of the sense amplifier, the voltage difference between
the sense nodes SAT and SAB can be increased to as large as V4. As a
result, the drop of the sense node SAT when the shared select signal SHL
is returned from the intermediate voltage VDL to the select voltage VPP
can be compensated by the overdrive voltage, thereby to quicken the
reading operation to the data input/output lines by the column select
signal YS.
FIG. 12 is a circuit diagram showing one embodiment of the sense amplifier
having the overdrive function. To the common source line CSP which is
connected with the sources of the P-channel MOSFETs Q7 and Q8 of the sense
amplifier, there is added not only the power switch MOSFET Q15 but also
the N-channel MOSFET Q16 forming the overdrive portion. This MOSFET Q16
operates to feed the power voltage VDD to the common source line CSP in
response to the timing signal SAP2. In order to output the power voltage
VDD from the source of the MOSFET Q16, the select level of the timing
signal SAP2 to be fed to the gate is set to a voltage as high as the
boosted voltage VPP.
In order to lighten the dependency of the sense amplifier operating speed
upon the power voltage VDD, the boosted voltage VPP may be applied, as the
overdrive voltage, in place of the power voltage VDD, as fed from the
external terminal, to the gate, and the drain may be connected with the
power voltage VDD so that voltage slightly dropped from the power voltage
VDD may be used from the source. By adding such an overdrive portion, in
response to the timing signal SAP2, the potential of the common source
line CSP or the operating voltage of the sense amplifier can be
temporarily raised to a voltage as high as VDD.
FIG. 13 is a schematic element layout diagram showing one embodiment of the
sense amplifier portion to be used in the dynamic RAM according to the
invention. In this embodiment, the power switch MOSFETs Q14 and Q15 for
driving the sense amplifier are dispersed and arranged along the sense
amplifier array. In other words, the power switch MOSFETs Q14 and Q15 are
not arranged together to have a large size in the cross area, as described
hereinbefore, but are dispersed in the sense amplifier array to have a
small element size.
In this embodiment, although the invention is not especially limited
thereto, the two MOSFETs Q14 and Q15 are arranged to correspond to the
sixteen unit circuits. A specific description will be made by taking up
the unit circuit on the left hand as an example. There are arranged
consecutively from the upper side: the shared switch MOSFETs Q1 and Q2;
the MOSFETs Q10 to Q12 forming the precharge circuit; the switch MOSFETs
Q12 and Q13 forming the column select circuit; the P-channel amplify
MOSFETs Q7 and Q8 forming the CMOS latch circuit; the N-channel amplify
MOSFETS Q5 and Q6 forming the CMOS latch circuit across the region forming
the power switch MOSFETs Q14 and Q15; and the shared switch MOSFETs Q3 and
Q4.
In order to elongate the gate along the sense amplifier array, the power
switch MOSFETs Q14 and Q15 are provided to have a larger channel width
than that of the shared switch MOSFETs, that is, to have a larger element
size thereby to allow a larger current to flow therethrough. In this case
the MOSFET Q14 for driving the common source line CSN of the N-channel
MOSFETs is fed at its gate with a relatively low potential such as VDL so
that it is made to have a larger size than that of the MOSFET Q15 having a
gate supplied with the power voltage VDD or the boosted voltage VPP. When
the power switch MOSFETS for driving the sense amplifier are thus
dispersed and arranged, the distance between the sense nodes and the power
switch MOSFETs can be shortened to equalize the operation timings of the
plurality of sense amplifiers provided in the sub array and to utilize the
cross area effectively for another circuit.
FIG. 14 is a timing chart for explaining another example of the reading
operation of the dynamic RAM according to the invention. In this
embodiment, the timing chart is shown to correspond to the example in
which the shared switch MOSFETs are made of P-channel MOSFETs. When the
shared switch MOSFETs are made of the P-channel MOSFETs, the select level
is set to the earth potential, e.g., VSSA of the circuit, and the unselect
level is set to a voltage such as the dropped voltage VDL corresponding to
the high level of the bit lines.
Therefore, the shared select signal SHL to be fed to the shared switch
MOSFETs on the selected side is set to the potential which corresponds to
the half precharge voltage VBLR such as VDL/2 after the sub word line SWL
was selected so that the read voltage difference appears at the sense
nodes SAT and SAB of the sense amplifier. When the potential difference
between the sense nodes SAT and SAB is enlarged by the amplifying
operation of the sense amplifier, the potential on the bit line BLLT on
the high level side is raised by the switch MOSFET Q1 which is made to
have a relatively low gate potential and which is connected with the bit
line BLT on the high level side, thereby to enlarge the potential
difference between the sense nodes SAT and SAB.
When these P-channel MOSFETs are used as the shared select MOSFETs to
increase the signal amount on their high level side, it is desirable to
set the precharge potential of the data input/output lines to the earth
potential side and to cause the CMOS latch circuit constructing the main
amplifier to perform the amplifying operation by the P-channel MOSFETS.
When the main amplifier of FIG. 5 is used, more specifically, the
operating voltage such as VDL is fed to the source sides of the P-channel
MOSFETs Q24 and Q25 by the P-channel MOSFETS, and the earth potential of
the circuit is fed to the sources of the N-channel MOSFETs Q21 and Q22. As
a result, the,main amplifier can be operated in an excellent sensible
region in response to the output signal from the sense amplifier.
FIG. 15 is a circuit diagram showing the sense amplifier portion of another
embodiment of the dynamic RAM according to the invention. This embodiment
is exemplified by providing a pair of complementary bit lines in a manner
to correspond to the sense amplifier. When the paired complementary bit
lines BLT and BLB are thus assigned to the sense amplifier, too, bit line
cutting MOSFETs Q1' and Q2' are interposed between the bit lines and the
sense nodes SAT and SAB of the sense amplifier. Moreover, a control signal
BC to be fed to the gates of those MOSFETs Q1' and Q2' is changed, unlike
the-control of the ternary levels in the foregoing Japanese Patent
Laid-Open No. 4-167293, with the binary voltage between a select level
such as VPP and an intermediate potential such as VDL.
Even when these bit line cutting MOSFETs are provided, the sense output can
be quickly read out to data input/output lines IOT and IOB by controlling
the control signal BC not at the ternary level, as in the foregoing
Laid-Open, but at the binary level, as has been described above. These
data input/output lines IOT and IOB correspond, when the memory array is
divided into sub arrays, as described above, to the local input/output
lines and are connected by the selector circuit to the main input/output
lines provided with the main amplifier.
FIG. 16 is a waveform diagram for explaining the operations when the
invention is applied to a synchronous DRAM. FIG. 16 exemplifies the case
of the burst length BL=2 and a CAS latency CL=2. These valves BL=2 and
CL=2 are set in the mode register. For BL=2, two column switches are
read/written for two consecutive cycles, and for CL=2, the output data are
outputted from the output terminal DQ two cycles after the read command.
In response to a bank active command, an address signal of the row system
is fetched from the address input terminal and decoded to set the sub word
line SWL to the select level such as VPP. As a result, minute read signals
appear on the complementary bit lines BLT and BLB. Since the sense
amplifier is activated with the operation timing signal, the minute read
signals of the complementary bit lines BLT and BLB are amplified to a high
level such as VDL and to low level such as VSS so that the sub word line
SWL is reloaded (or refreshed) in the selected memory cell. Then, at the
start of the operation of the sense amplifier, the gate voltage of the
shared switch MOSFETs on the not-shown selected side is temporarily set to
the intermediate voltage, as described hereinbefore, and then returned to
the select level so that a refresh operation is executed.
After two cycles of the bank active command, a read command is inputted so
that an address signal of the column system not-shown is fetched to raise
a column select signal YS1. As a result, the main input/output lines MIOT
and MIOB are precharged to the VDL level just before the column selection,
and the necessary read voltage difference is obtained from the bit line
information of the YS selection and is amplified by the main amplifier, as
activated with the signal MAE, to generate an output signal MO. This
output signal MO of the main amplifier is a low amplitude signal
corresponding to the dropped voltage VPER1, as described hereinbefore, and
is shifted in its level to the VDD level at the input portion of the
output buffer so that it is outputted in synchronism with the output
timing signal DOC. For BL=2, the address of the Y system is switched in
synchronism with the next clock CLK of the read command so that the output
signal MO of the main amplifier is generated correspondingly.
The access time from the bank active command to the decision of the first
output signal DQ is tRACeq; the access time from the read command to the
decision of the output signal DQ is tAAeq; and the access time from the
clock signal CLK to the decision of the output signal DQ is tAC. According
to the invention, a necessary amount of read signal to the main amplifier
is quickly achieved at the time of the Y selecting operation so that the
access time tAC can be shortened. By the control with the high amplitude
signal, moreover, the current to flow to the MOSFETs to be driven thereby
can be increased to reduce the signal delay thereby to make a contribution
to the higher speed. As a result, the period of the clock signal CLK can
be accordingly shortened to raise the speed of the synchronous DRAM.
The following effects can be obtained from the foregoing embodiments. That
is:
(1) Switch MOSFETs are interposed between a sense amplifier disposed in a
dynamic RAM and complementary bit lines. After signal voltages were read
out by the selecting operations of said word lines from a plurality of
dynamic memory cells selected, to the plurality of pairs of complementary
bit lines in, accordance with their individual storage informations, the
switch control signal of said switch MOSFETs is changed from a select
level to the intermediate potential having (a): an OFF state or a
relatively high ON resistance for the signal voltage read out to said
complementary bit lines (b); an ON state with a relatively low resistance
for a potential at which the sense nodes are set to one level by the
amplifying operation of the sense amplifier; and (c) an OFF state at a
potential of the other level. The sense amplifier is supplied with an
operating voltage to start the amplifying operation in response to the
change in said switch control signal; an amplification signal generated by
said amplifying operation is transmitted through the column select circuit
to said input/output lines in response to the column select signal; and
said switch control signal is returned to the select level in response to
the selecting operation of said column select circuit. As a result, there
is provided an effect that the sense amplifying operation of a minute
signal can be performed stably and quickly, to output the amplified signal
at a high speed to the data input/output lines.
(2) A precharge circuit for precharging said complementary bit lines is
further provided at said sense nodes; and when said word lines are in an
unselected state, said switch control signal is set to a select level so
that the complementary bit lines are precharged through said switch
MOSFETs by the precharge circuit disposed at the sense nodes. As a result,
the sense amplifying operations of the minute signal can be performed
stably and quickly, and the amplified signal can be outputted quickly to
the data input/output lines. At the same time, the precharge circuit can
be shared between the sense nodes and the complementary bit lines thereby
to provide an effect that the circuit can be simplified.
(3) The complementary bit lines are arranged on the left and right of said
sense nodes; said switch MOSFETs are used with select switch MOSFETs of
said complementary bit lines arranged on the left and right; and the
switch control signal of the switch MOSFETs, corresponding to the
unselected complementary bit line, is set to an unselect level before said
word lines are selected. By using this shared sense construction, the
sense amplifying operations of the minute signal can be performed stably
and quickly, and the amplified signal can be outputted quickly to the data
input/output lines thereby to provide an effect that the circuit can be
simplified.
(4) Said switch control signal is returned in a gentle change from said
intermediate potential to the select level in response to the selecting
operation of said column select circuit. As a result, the signal voltage
on the other level side can be enlarged to provide an effect that the
sense amplifying operations of the minute signal can be performed stably
and quickly to output the amplified signal more quickly to the data
input/output lines.
(5) The main amplifier including the CMOS latch circuit having connected
input/output terminals is connected with said data input/output lines;
said data input/output lines are precharged to the other level of a
polarity reversed from that of one level of said sense nodes; and said
main amplifier feeds,.when it is brought into the operating state, said
CMOS latch circuit with an operating voltage corresponding to the other
potential. As a result, there is provided an effect that the main
amplifier made of the CMOS latch circuit can be operated with a high
sensitivity.
(6) Said word lines include a main word line and a plurality of sub word
lines assigned commonly to said main word line; the gates of the address
select MOSFETs of said dynamic memory cells are connected with said sub
word lines; one of said sub word lines is selected by a sub word driver
which receives the signal of said main word line and the signals of said
sub word selecting lines; said sub word driver generates a select signal
of the sub word lines which are disposed on the left and right sides
excepting the end portions of the memory cell array; and said sense
amplifier senses the amplified signals from the complementary bit lines
which are disposed on the left and right sides, except for the end
portions of the memory cell array. As a result, there is provided an.
effect that a dynamic RAM having a large storage capacity can be realized
to stabilize the sense amplifying operation of the minute signal and to
output the amplified signal at with high speed nto the data input/output
lines.
(7) The operating voltage to be fed to said sense amplifier is a dropped
voltage which is dropped from the power voltage fed from an external
terminal; the select level of said word lines and the select level of said
switch MOSFETs are a boosted voltage which is boosted from said power
voltage; and said intermediate potential uses the dropped voltage
corresponding to the operating voltage of said sense amplifier. As a
result, there is provided an effect that the sense amplifying operation of
the minute signal can be stabilized and quickened without any addition of
a special internal power circuit, thereby to output the amplified signal
to the data input/output lines at a high speed.
Although our invention has been specifically described in connection with
various exemplary embodiments, it should not be limited to those
embodiments but can naturally be modified in various manners without
departing from the gist thereof. In the dynamic RAM shown in FIG. 1 or 2,
for example, the construction of the memory array, the sub array and the
sub word driver can take a variety of modifications, as exemplified by a
word shunt construction using no sub word driver. The power switch MOSFET
Q15 for applying the operating voltage VDL to the sense amplifier may be
exemplified by a P-channel MOSFET.
The operating voltage of the sense amplifier may use the power voltage fed
from the external terminal, as it is. The intermediate voltage of this
case may use a half precharge voltage or may utilize a voltage generated
especially therefor. The main amplifier may utilize a differential
amplifier in addition to the one using the CMOS latch circuit. The
invention can be widely utilized in a semiconductor memory device using
the dynamic memory cells, such as the semiconductor memory device to be
packaged over a digital integrated circuit such as a microcomputer.
The effects to be obtained by the representative aspects of the invention
disclosed herein will be briefly described in the following. Specifically,
switch MOSFETs are interposed between a sense amplifier disposed in a
dynamic RAM and complementary bit lines. After signal voltages were read
out by the selecting operations of said word lines from a plurality of
dynamic memory cells selected, to the plurality of pairs of complementary
bit lines in accordance with their individual storage informations, the
switch control signal of said switch MOSFETs is changed from a select
level to the intermediate potential having: (a) an OFF state or a
relatively high ON resistance for the signal voltage read out to said
complementary bit lines; (b) an ON state with a relatively low ON
resistance for a potential at which the sense nodes are set to one level
by the amplifying operation of the sense amplifier; and (c) an OFF state
at a potential of the other level. The sense amplifier is supplied with an
operating voltage to start the amplifying operation in response to the
change in said switch control signal; an amplification signal generated by
said amplifying operation is transmitted through the column select circuit
to said input/output lines in response to the column select signal; and
said switch control signal is returned to the select level in response to
the selecting operation of said column select circuit. As a result, the
sense amplifying operation of a minute signal can be performed stably and
quickly, and the amplified signal can be outputted at a high speed to the
data input/output lines.
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